Defining optimal thickness for maximal self-field Jc in YBCO/CeO₂ multilayers grown on buffered metal

Abstract

The effect of multilayering YBa2Cu3O6+x (YBCO) thin films with sequentially deposited CeO2 layers between YBCO layers grown on buffered metallic template is investigated to optimize the self-field critical current density J c(0). We have obtained that the improvement in J c(0) clearly depends on the YBCO layer thickness and temperature, where at high temperature J c(0) can be increased even 50 % when compared with the single layer YBCO films. Based on our experimental results and theoretical approach to the growth mechanism during multilayer deposition, we have defined a critical thickness for the YBCO layer, where the maximal self-field J c(0) is strongly related to the competing issues between the uniform and nonuniform strain relaxation and the formation of dislocations and other defects during the film growth. Our results can be directly utilized in the future coated conductor technology, when maximizing the overall in-field J c(B) by combining both the optimal crystalline quality and flux pinning properties typically in bilayer film structures.

Enhanced Critical Current Density in Heterostructural YBCO/Ca-Doped YBCO Multilayers

“…In contrast, for example, when using a CeO 2 interlayer, a strained region of several nanometers thick consistently forms above the CeO 2 interlayer. 56 Finally, based on the literature, the partial substitution of Ca 2+ ions at Y 3+ sites in YBCO alters the carrier concentration and affects the transfer of charges from the CuO chains to the conducting CuO 2 planes. 57,58 The fixed charge is entirely offset by oxygen defects, resulting in a slightly reduced equilibrium oxygen content, which also contributes to a lower superconducting transition temperature.…”

“…These techniques have been shown to enhance the crystalline quality of each sublayer, reducing the likelihood of defect formation in subsequent deposition intervals. 55,56 Second, the underlying Ca-doped YBCO layer serves as an ideal foundation for the 4% BZO-doped YBCO layer. Notably, Ca-doped YBCO exhibits average in-plane and out-of-plane lattice parameters (a = 3.83 Å, b = 3.88 Å, and c = 11.71 Å) that closely match those of BZO-doped YBCO.…”

“…This is evident in earlier shown TEM images (see Figure b,c), where the growth of BZO-doped YBCO directly above the Ca-doped YBCO layer occurs smoothly, epitaxially through the interface, without the presence of any distorted layers next to it (Figure b). In contrast, for example, when using a CeO 2 interlayer, a strained region of several nanometers thick consistently forms above the CeO 2 interlayer …”

“…Previously, we both experimentally and theoretically determined that the crystalline quality of YBCO thin films can be enhanced through the use of multilayering (Figure a). This, in turn, extends the electron mean free path and consequently, the self-field J c (0). − Utilizing a multilayer structure allows for precise control over critical factors such as uniform and nonuniform strain relaxation, as well as the formation of dislocations and other defects in layers with constrained thicknesses. This approach offers the opportunity to increase the overall thickness of the film, while maintaining improved crystalline properties.…”

Enhanced critical current density in optimized high-temperature superconducting bilayer thin films

“…Consequently, it can be greatly affected by the deposition process. As an example, we have previously shown that the PLD process can be modified to produce APC-free YBCO films with significantly higher crystalline quality [31,32]. While the condition J c,v (f = 0) = 0 persists to hold for an ideal YBCO film at all temperatures, its validity even for the highest quality experimentally produced YBCO films can be questioned at high temperature range.…”